1. Field of the Invention
This invention relates generally to the art of metal recovery and more particularly to a method and means of recovering silver from the developing process of photographic film.
2. Description of the Prior Art
The most efficient and practical method of recovering silver from spent silver solution containing silver such as from film developing solution is by means of the electroplating method which is accomplished by use of commercially available silver recovery units. These units are supplied with a flow of solution from, for example, the fixer overflow section of a film developer. Such silver recovery units are commercially available and operate on the silver plating principle. Such units generally contain for its silver recovery means, anode and cathode members submerged in a bath of solution containing silver through which an electric current is charged whereby silver is deposited onto the cathode from the solution and from which, from time to time, the silver plated on the cathode is removed therefrom. The particular problem of the prior art that this invention is intended to alleviate is the problem commonly associated with prior art method and means used to recover silver from the process of developing X-ray film in hospital operations. Hospital practice generally expose and develop a majority of its X-ray film during the morning hours. Consequently, the film developing equipment and the silver recovery equipment which operate in conjunction therewith generally are not in operation during the evening or night hours. If the operating attendant does not put in operation the silver recovery equipment at the same time that the film developing equipment is put in operation, the silver laden solution is wasted down the drain. Also, since the prior art method includes the step of providing the silver recovery unit with silver laden fixer solution directly from the film processing unit, the silver laden solution will contain varying concentration of silver. Since the silver recovery unit operates on a preselect current, this preselect current may be insufficient or excessive for the amount of silver in the solution at the moment of flow therethrough. If the current is insufficient for the silver concentration flowing through the unit, silver recovery will be incomplete and silver will be wasted in that all of it will not be precipitated onto the cathode. On the other hand, if there is insufficient silver in the solution for the current which is preset on the silver recovery unit, the current will burn the silver and diminish its value. Another variable inherent in the prior art process of recovering silver by the electroplating method is the rate of flow of the silver laden solution. If a large quantity of film is required to be processed within a limited time, the rate of flow is increased which results in silver being lost even though the current is adequate for the silver solution concentration since this has the same effect as when the current is insufficient.
These variables which are inherent in the prior art method of recovering silver, that is: (1) irregular concentration of silver in the fixer overflow solution resulting from irregular film processing, (2) irregular flow of silver laden solution from the processor to the silver recovery unit resulting from direct feeding of the solution, and, (3) due to human error, failure to operate the film processing unit and the silver recovery unit at the same time, all contribute to wasting of silver metal.